geode-core/src/main/java/org/apache/geode/internal/cache/partitioned/rebalance/RebalanceDirector.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more contributor license
 * agreements. See the NOTICE file distributed with this work for additional information regarding
 * copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the License. You may obtain a
 * copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */
package org.apache.geode.internal.cache.partitioned.rebalance;


import org.apache.geode.internal.cache.partitioned.rebalance.model.PartitionedRegionLoadModel;

/**
 * A class that is responsible for directing all or part of a rebalance operation. The director
 * receives a model of the current system, and requests changes to the system such as creating
 * buckets, moving buckets, or moving primaries.
 *
 *
 */
public interface RebalanceDirector {

  /**
   * A check to see if rebalancing is necessary on the given region. This is called before the
   * initialize method is called with the model it is here so that directors can cause the rebalance
   * to early out before gathering extra information.
   *
   * @param redundancyImpaired true if redundancy is impaired for the PR
   * @param withPersistence - true if persistence is enabled for the PR
   *
   * @return true if the rebalance should continue.
   */
  boolean isRebalanceNecessary(boolean redundancyImpaired, boolean withPersistence);

  /**
   * Initialize the director with the model of the PR. This model is gathered from the peers and
   * passed to this callback before the rebalancing starts. The director can build any initial state
   * it needs from the model at this point.
   */
  void initialize(PartitionedRegionLoadModel model);

  /**
   * Called when a membership change has invalidated the old model and created a new model. The
   * director should switch to the new model and reinitialize it's state as appropriate.
   */
  void membershipChanged(PartitionedRegionLoadModel model);

  /**
   * Perform one step of the rebalancing process. This step may be to create a redundant bucket,
   * move a bucket, or move a primary.
   *
   * This method is expected to attempt one small unit of rebalancing work. When the method returns,
   * the system will check to see if the model is still accurate. If true is returned, the
   * PartitionedRegionRebalanceOperation will come back and call nextStep again. It's not required
   * that a move is actually performed during the nextStep call, just that nextStep will return
   * false once there is no more work to be done.
   *
   * It is expected that nextStep will eventually return false.
   *
   * @return true we were able to make progress or at least attempt an operation, false if there is
   *         no more rebalancing work to be done.
   */
  boolean nextStep();
}